The present invention relates, in general, to mechanical resonators, and more particularly to tunable micromechanical devices wherein the resonant frequency of oscillators and resonators can be selectively increased and decreased.
In the field of electromechanical filters, high Q mechanical resonators are used to pass frequencies very close to the resonant frequency of the mechanical structure. Pass band filters can be constructed using resonators in parallel, where the resonant frequencies of two or more resonators are close together. However, even apparently identical micromechanical devices such as oscillators or resonators have variations in their resonant frequencies, even when they are fabricated on the same die, because of differences in materials dimensions, and the like from one device to the next, and due to drift over a period of time. This inhibits the reproduceability and the quality of such devices, and results in the need for a method or structure for tuning their resonant frequencies quickly, easily, and reliably.
Pass band filters have been constructed which utilize a series of resonators in parallel, but techniques for adjusting their resonant frequencies require the use of processes such as laser trimming and selective deposition (see "Microelectromechanical Filters for Signal Processing," Liwei Lin et al, proceedings IEEE Microelectromechanical Systems (Travemunde, Germany) February 1992, pages 226-231. See also Electromechanical Dynamics part III: Elastic and Fluid Media, Herbert H. Woodson et al, Robert E. Kreger Publishing Co., 1985, pages 704-707). Such techniques have not been entirely satisfactory. In addition, previous work on the theory of electrostatic tuning actuators and their associated nonlinearities has been done, but such work only addresses resonant frequency reduction, not augmentation.